On a printed circuit board (PCB), electric wirings connecting various components are expressed by wiring figures in accordance with circuit design. The printed circuit board (PCB) serves to connect and support various components. These printed circuit boards are classified into a rigid printed circuit board, a flexible printed circuit board, a rigid-flexible printed circuit board made by combining the two boards, and a multi-flexible printed circuit board similar to the rigid-flexible printed circuit board.
A flexible metal-clad laminate is manufactured by laminating a polymer film layer and a metal conductive layer, and is characterized by having flexible properties. This flexible metal-clad laminate is mainly used in electronic devices or materials of the electronic devices requesting flexibility or pliability. The thickness of the polymer film layer may be requested to be variously changed depending on the usage thereof. Among them, the demand for a thick metal-clad laminate having a thick polymer film layer is largely growing in fields in which electric properties of high reliability are needed, such as the aerospace industry and a transmission of vehicles.
With respect to this technology, the flexible metal-clad laminate of the related art mainly employs a method of laminating a film type thermoplastic polyimide onto a metal foil, and a method of directly coating a polyamic acid varnish on a metal foil. However, both of these methods have advantages and disadvantages. In the laminating method, since the already cured polyimide film is used during a manufacturing procedure, the thickness thereof does not greatly affect workability. However, the material cost of the polyimide film is comparatively high and considering that it is general to use a thermoplastic polyimide having a high coefficient of linear thermal expansion, a dimensional change is large when the thermoplastic polyimide is subjected to a high temperature process such as component mounting. Whereas, according to the manufacturing method conducted by casting a polyimide precursor, the polyimide film can be manufactured with a lower material cost and even though thermosetting polyimide having relatively low coefficient of linear thermal expansion is used, it can achieve a sufficient adhesiveness with a metal layer and thus, allowing an excellent dimensional stability even at a high-temperature process. However, as the thickness of the polyimide gets increased, blister and film curl severely occur while the solvent contained in the polyamic acid varnish is vaporized, and thus, the manufacture thereof is difficult.